INN Telmisartan is an angiotensin II receptor antagonist developed for the treatment of hypertension and other medical indications as disclosed in EP-A-502314. Its chemical name is 4′-[2-n-propyl-4-methyl-6-(1-methylbenzimidazol-2-yl)-benzimidazol-1-ylmethyl]-biphenyl-2-carboxylic acid having the following structure:

Telmisartan is generally manufactured and supplied in the free acid form. As disclosed in WO 00/43370, crystalline telmisartan exists in two polymorphic forms having different melting points. Under the influence of heat and humidity, the lower melting polymorph B transforms irreversibly into the higher melting polymorph A. Both forms are characterized by a very poor solubility in aqueous systems at the physiological pH range of the gastrointestinal tract of between pH 1 to 7.
Telmisartan is obtainable on the market under the trade name Micardis®. Starting from the free acid form Telmisartan as introduced to the market is manufactured using an expensive spray-drying process. Due to the poor solubility of the free acid form preparation of alternative telmisartan formulation is difficult.
Diuretics such as amiloride, chlorothalidone, furosemide, hydrochlorothiazide, indapamide and piretanide are therapeutic agents used in the treatment of edema and hypertension. Occasionally they are combined with anti-hypertensive agents acting on the basis of a different mode of action to achieve synergistic therapeutic efficacy in the treatment of hypertension. A preferred diuretic is hydrochlorothiazide (HCTZ). The chemical name of HCTZ is 6-chloro-3,4-dihydro-2H-1,2,4-benzothiadiazine-7-sulfonamide-1,1-dioxide having the following structure

It is an object of the present invention to provide a fixed dose combination drug comprising telmisartan and a diuretic such as HCTZ displaying the required fast dissolution and immediate drug release profile combined with adequate stability. Generally, a fixed-dose combination of drugs intended for immediate release is prepared by either making a powder mixture or a co-granulate of the two active ingredients with the necessary excipients, normally keeping the basic formulation of the corresponding mono-drug preparation and simply adding the second drug component.
With a combination of telmisartan and HCTZ, this approach was not feasible due to the incompatibility of HCTZ with basic compounds such as, e.g., meglumine (N-methyl-D-glucamine) which is a component of conventional telmisartan formulations, and the reduced dissolution rate of HCTZ from a dissolving matrix as compared with dissolution from a disintegrating tablet matrix.
Several galenical approaches to overcome the incompatibility problem have been investigated. A classical approach is to coat the HCTZ particles in a fluidized-bed granulator with a polymer solution containing water soluble polymers like hydroxypropylcellulose, hydroxypropylmethylcellulose or polyvinylpyrrolidone, thereby reducing the contact surface area of the HCTZ particles with the telmisartan formulation during mixing and compressing. Yet, by these means it was not possible to reduce the contact area of HCTZ with the telmisartan formulation in a compressed tablet to a degree sufficient to achieve the desired prolonged shelf life.
Furthermore, the dissolution rate of HCTZ from tablets comprising coated HCTZ in a telmisartan formulation was further reduced due to the gel-forming properties of the polymer.
Another approach was to produce separate film-coated tablets for telmisartan and HCTZ in such a size and shape that these could be filled into a capsule. By dividing the doses into two to four single small tablets for telmisartan and into one or two small tablets for HCTZ, a capsule of size 1 to 0 long could be filled. Yet, with this approach the drug dissolution rate of telmisartan was reduced compared to the single entities due to a lag-time effect of the large capsule shells. Furthermore, with regard to patients' compliance a zero long capsule is not deemed reliable.